• Nuclear Engineering and Technology
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• 제34권4호
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .

• 한국군사과학기술학회지
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• 제6권4호
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• pp.100-112
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• 2003

This paper presents the transient response analysis of a rotating blade in resonant frequency range. It is shown that the modeling is considered in elastic foundation and friction damping effect. The equations of motion are derived and transformed into a dimensionless form to investigate general phenomena. Numerical results show that the magnitude of friction damping to reduce maximum transient response in near the critical angular speed. The method can be applied to a number of examples of the practical rotating blade system to minimize transient response in resonant frequency range.

• 컴퓨터교육학회논문지
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• 제19권2호
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• pp.99-114
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• 2016

일시적 정보효과는 멀티미디어 학습 환경에서 길고 복잡한 청각적 정보의 일시성으로 인해 학습에 가해지는 부정적인 효과를 말한다. 본 연구는 인지부하이론의 틀에서 멀티미디어 학습에서 일시적 정보효과가 학습에 미치는 영향을 살펴보고, 또한 일시적 정보효과를 극복하는 방법인 것으로 생각되는 분절화(long vs. short)와 학습자료 제시 조절방법(system-paced vs. learner-paced)이 일시적 정보효과에 어떤 영향을 미치는 지 살펴보고자 하였다. 연구결과에 의하면 멀티미디어 학습 환경에서 길고 복잡한 학습자료를 학습자에게 제시할 경우에는 시각적으로만 제시하는 것이 시청각적으로 제시하는 것보다 학습효율성이 보다 높은 것(높은 성취와 낮은 인지부하 투입)으로 드러났다. 또한 시청각적으로 자료를 제시해야 하는 경우는 청각적 학습 자료를 분절화해서 제시하거나, 학습자료 제시를 학습자가 조절하는 방법으로 멀티미디어 학습 환경을 설계하는 것이 학습 효율성을 높이는 방안인 것으로 드러났다.

• 전기학회논문지
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• 제59권9호
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• pp.1611-1614
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• 2010

The explosion of a nuclear weapon radiates a gamma-ray in the form of a transient pulse. If the gamma-ray introduces to semiconductor devices, much Electron-Hole Pairs(EHPs) are generated in depletion region of the devices[7]. as a consequence of that, high photocurrent is created and causes upset, latchup and burnout of semiconductor devices[8]. This phenomenon is known for Transient Radiation Effects on Electronics(TREE), also called dose-rate effects. In this paper 3D structure of inverter and NAND gate device was designed and transient pulse gamma-ray was modeled. So simulation for transient radiation effect on inverter and NAND gate was accomplished and mechanism for upset and latchup was analyzed.

• 전기학회논문지
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• 제61권10호
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• pp.1448-1453
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• 2012

In this study, we carried out transient radiation test for identify failure situation by a transient radiation effect on operational amplifier devices. This experiments were carried out using a 60 MeV electron beam pulse of the LINAC(Linear Accelerator) facility in the Pohang Accelerator Laboratory. In this test, we has found that a serious failure as a burn-out effect due to overcurrent on the partial electronic devices.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.1798-1806
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• 2018

When a contingency occurs in a large transmission route in a power system, it can generate various instabilities that may lead to a power system blackout. In particular, transient instability in a power system needs to be immediately addressed, and preventive measures should be in place prior to fault occurrence. Measures to achieve transient stability include system reinforcement, power generation restriction, and generator tripping. Because the interpretation of transient stability is a time domain simulation, it is difficult to determine the efficacy of proposed countermeasures using only simple simulation results. Therefore, several methods to quantify transient stability have been introduced. Among them, the single machine equivalent (SIME) method based on the equal area criterion (EAC) can quantify the degree of instability by calculating the residual acceleration energy of a generator. However, method for generator tripping effect evaluation does not have been established. In this study, we propose a method to evaluate the effect of generator tripping on transient stability that is based on the SIME method. For this purpose, the measures that reflect generator tripping in the SIME calculation are reviewed. Simulation results obtained by applying the proposed method to the IEEE 39-bus system and KEPCO system are then presented.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.75-81
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• 2000

To provide the appropriate direction for development of transient control in a gasoline engine, transient performance analysis and evalution under four accelerating types based on typical driver's acceleration type were implemented by experimental study. In order to evaluate the characteristics of transient performance quanititatively, the concept and method by transient response specifications were introduced. Several performance parameters in terms of engine speed(RPM), manifold absolute pressure(MAP), fuel injection duration($\DeltatI_{nj}$) and air excess ratio($\lambda$) were emasured simultaneously during the four types of the throttle valve opening with the step motor controlled by PC. The result showed that transient response specifications in terms of delay time, rising time and settling time characterized the transient performance for four acceleration types quantitatively. Intensified acceleration type was most economical and linear acceleration type revealed the best emission performance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.226-227
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• 2006

Wind power is one of the fastest growing distributed generation types. As part of a worldwide trend, the concerns of large wind generation have been risen rather than small wind generation since it influences the whole power system Including the transient stability. The objective of this paper is to understand the effect of a large-scale wind generation on power system transient stability and to develop a systematic procedure to assess the effect according to the location and capacity of a wind farm. In the proposed procedure, an index is presented to evaluate the appropriateness of the location and capacity of a wind farm for transient stability contingencies.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 학술대회 논문집
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• pp.399-403
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• 2005

In this paper, we analyze on the effect of RC filter to mitigate transient overvoltage on the high voltage induction motor fed by H-bridge cascaded 7-level inverter. The switching surge voltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. The effect of switching surge appears more serious in high voltage induction motor than low voltage induction motor. Consequently, we demonstrated that the RC filter connected to the motor terminals greatly reduces the transient voltage stress md ringing. The results of simulation show the suppression of transient overvoltage at the motor end of a long cable. using EMTP

• ETRI Journal
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• 제25권6호
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• pp.531-534
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• 2003

This report describes the effect of optical delay on the suppression of the power transient excursion in a combined gain-controlled erbium-doped fiber amplifier with an internal optical feedback loop (OFL). A simple homogeneous model showed that the optical delay caused a phase change in the oscillation of the surviving and laser channels, which resulted in a reduction of the overall power transient excursion. In addition to the reduction, a real system with a 1528.7-nm OFL shifted the oscillation upward or downward according to channel removal or addition, whereas another one with a 1560.9-nm OFL did not. This different transient behavior reflected a control-wavelength dependence on optical automatic gain control, where spectral-hole burning dominated over relaxation oscillation for 1528.7 nm, and vice versa for 1560.9 nm.